| AVS 61st International Symposium & Exhibition | |
| 2D Materials Focus Topic | Thursday Sessions |
| Session 2D+EM+MI+MN+NS+SS+TF-ThA |
| Session: | Novel Quantum Phenomena in 2D Materials |
| Presenter: | Hokwon Kim, Univ. Grenoble Alpes/ CEA, LETI, France |
| Authors: | H. Kim, Univ. Grenoble Alpes/ CEA, LETI, France A. Tyurnina, Univ. Grenoble Alpes/ CEA, LETI, France J.-F. Guillet, Univ. Grenoble Alpes/ CEA, LITEN, France J.-P. Simonato, Univ. Grenoble Alpes/ CEA, LITEN, France J. Dijon, Univ. Grenoble Alpes/ CEA, LITEN, France D. Rouchon, Univ. Grenoble Alpes/ CEA, LETI, France D. Mariolle, Univ. Grenoble Alpes/ CEA, LETI, France N. Chevalier, Univ. Grenoble Alpes/ CEA, LETI, France O.J. Renault, Univ. Grenoble Alpes/ CEA, LETI, France |
| Correspondent: | Click to Email |
The precise control of graphene’s conductivity and work function is crucial in developing practical applications of graphene based electronics. In order to enhance the conductivity of graphene, we employed a simple doping method where graphene films produced by chemical vapor deposition and transferred onto SiO2, Al2O3, and WO3 substrates are p-doped with iodine vapor through physisorption at temperature of ~ 100 °C [1-3]. The work function values and iodine to carbon ratios of the one-layer (1L) and two-layer (2L) folded regions were analyzed by high spatial- and energy resolution X-ray photoelectron emission microscopy (XPEEM) on a NanoESCA instrument. After the iodine doping, the work function values were significantly increased up to ~0.4 eV and ~0.5 eV, respectively, for 1L and 2L graphene on SiO2/Si. This higher degree of doping by iodine was corroborated by I 3d5/2 core level imaging of the same area where the 2L graphene exhibited significantly larger concentration of iodine (2 at. % versus 1 at. %) likely due to the intercalation of iodine at the inter-layer space.
The main iodine species identified by high resolution core level X-ray photoemission spectroscopy and Raman spectroscopy were I3- and I5- poly-iodide anionic complexes with slightly higher concentration of I5- in 2L than 1L graphene possibly due to different doping mechanisms. Temperature dependent ultra-high-vacuum, in-situ annealing of the doped films has demonstrated that most of iodine is removed above 300 °C for the both 1L and 2L regions, although a significant removal of iodine is observed for 2L graphene at temperature as low as 100 °C. Surprisingly, after the complete removal of iodine by annealing, the work function value did not return to the original one before the doping treatment and remained at a much higher value. This can be ascribed to the residual hydrocarbon contaminations interacting with the atomic defects within the graphene layer that lead to unintentional n-type doping in our samples[4].
Acknowledgement: The XPEEM and KFM measurements were performed at the Nanocharacterization Platform (PFNC).
References
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[4] B.H. Kim, S.J. Hong, S.J. Baek, H.Y. Jeong, N. Park, M. Lee, S.W. Lee, M. Park, S.W. Chu, H.S. Shin, J. Lim, J.C. Lee, Y. Jun, Y.W. Park, Sci. Rep., (2012).